Photosensitive light control system



March 3, 1964 G. SCHRENK ETAL PHOTOSENSITIVE LIGHT CONTROL SYSTEM FiledSept. 14. 1960 1 A B 6' D 1 Map. DEMdD i I 4.0. 52 i AMP. 5/ l l T 1 c.4 /5

ATTORNEYS ice United States Patent PHOTOSENSITIVE LIGHT CONTROL SYSTEMGotthilf Schrenk and Herbert Krappatsch, Erlangen, Germany, assignors toP. Gossen & Co. G.m.b.H.,

Erlangen, Germany Filed Sept. 14, 1960, Ser. No. 56,007 Claims priority,application Germany June 18, 1960 6 Claims. (Cl. 250-217) The presentinvention relates to an exposure meter or exposure control apparatus.

Photoelectric exposure meters are known for cameras in which theexposure is controlled in accordance with the light intensity present ona light-responsive element, which supplies a current to a sensitivecurrent meter, whose movable part operates the diaphragm opening. Thesemechanisms have the shortcoming that, due to the weakness of the currentsupplied by the light-responsive element, very small forces areavailable for actuating or setting the diaphragm, so that the lattermust be very easily movable and of light weight. This, in turn causesdisturbances to occur quite readily. -Also, such mechanisms are notsufficiently sensitive.

It is an object of the present invention to overcome the above mentioneddisadvantages.

This is accomplished in accordance with the invention by an automaticexposure control device which is constructed as follows. The source oflight causing the exposure is combined with a light intensity varyingdevice which is adjustable depending on the light intensity prevailingon a light-responsive element. The adjustment is made by setting to acertain value the voltage drop caused by the light striking the element.The voltage drop is compared with another voltage drop, and thedifference, after having been amplified, is fed to an electric motor,which either causes the light-responsive element to be covered by meansof an aperture control member, or which causes more light to fall on thelightresponsive element, thus making the voltage difference equal tozero, and simultaneously adjusts the light-intensity varying device.

(I he control mechanism according to the invention consists of a circuitwith two resistors arranged in series and a D.C. amplifier, one of theresistors being in parallel with the light-responsive element, the otherresistor being in parallel with -a source of comparison voltage, thearrangement being such that the resistors are traversed by currents inopposite directions. An electric motor is connected to that terminals ofthe D.C. amplifier, which motor moves an aperture control member infront of the light-responsive element and thereby re-adjusts the lightcontrolling mechanism.

The invention and its objects and advantages will be fully understoodfrom the following description and the drawings, in which:

FIGURE 1 illustrates schematically the automatic exposure meteraccording to the invention;

FIGS. 2 and 3 illustrate different embodiments of the invention of FIG.1; and

FIG. 4 illustrates another reference voltage source which may beemployed with the invention.

Referring to the drawings, light-responsive element 1 controls theexposure in accordance with light impinging thereon. In parallel withelement 1 there is a resistor 2 which is in series with a secondresistor 3 forming a circuit from a point A to a point B.

Parallel to resistor 3 is a constant voltage source 4, the arnangementbeing such that the direction of the voltage drop across resistor 3 isopposite to the voltage drop caused by the current of thelight-responsive element 1 across resistor 2. Points A and B are theinput terminals 3,123,724 Patented Mar. 3, 1964 "ice of a DC. amplifier5, whose output terminals are C and l), connected to an electric motor6. This motor moves a cover member 7 over element 1. Rigidly connectedwith member 7 is a gear wheel 8 which engages with another gear wheel 9,which in turn is secured to the ring of the iris diaphragm 10 of thecamera. Member 7 carries a marker or index L1 which moves over a scale12 graduated preferably in light values. An equalizing resistor 13,which may be fixed or adjustable to different values, is connectedbetween the current source 4 and resistor 3. A light impermeable member14 is mounted in fixed relationship to light-responsive element 1 toserve as a variable width mask therefor.

The arrangement operates as follows:

When the light-responsive element 1 is lighted, a voltage drop occursacross resistor 2, which is opposite to the voltage drop across resistor3. When the two voltage drops are not equal, the amplifier 5 transmitsthe difference, in amplified form and with the resulting polarity, toelectric motor 6. The motor then rotates in one direction or the other,depending on the transmitted polarity, in such a manner that the element1 is further exposed or further covered, depending on whether the dropis smaller in resistor 2 than in resistor 3 or vice versa. When the twovoltage drops become equal, the amplirifer 5 no longer supplies anycurrent. The motor 6 and the aperture control element 7 are then atrest. Simultaneously with the turning of member 7, motor 6 turnsdiaphragm 10 into the position corresponding to the prevailing light,which is done through gears S and 9.

The amplifier considerably increases the sensitivity of the instrumentand consequently a sensitive meter is no longer required. Moreover, astructure is obtained which is mechanically much more sturdy.

In order to avoid drift errors, it is desirable to provide the DC.amplifier 5 with a modulator 50', an AC. arnplirfier 51, and ademodulator 52. This type of arrangement is old and well known. inoperation, when a differential direct voltage appears on leads LA and B,it is converted by modulator 50 into an alternating voltage having arectangular waveform. This alternating voltage is amplified in amplifier51 and then re converted into an amplified direct voltage of the properpolarity by demodulator S2. The components themselves, and the manner inwhich they are arranged, are well known in the electrical arts. Circuitsuseful as such components are described in the following publications:(a) Trans. AJ 74 (1955) pt. #1. ppu141-149, Switching Transistors Usedas Substitute for Mechanical Low-level Choppers, A. P. Kruper; '(b)Proc. (1958) pp. 258-266, A Transistor High-Gain-Chopper-Type D.C.Amplifier, G. B. B. Chaplin and A. R. Owens; (0) Proc. J.E.E., paper No.2368 R; May 1957, Milnes, D. Sc.

One advantage of the apparatus of the invention is that the variablemasking of element 1 affords the possibility of realizing a desirablefunctional interdependence of the light intensity on element -1 and theposition of diaphragm 10, by appropriately shaping the aperture cover 7or light-responsive element 1, or both members. For the same purpose,the cut-out portion of member 14 can be varied as desired. In a similarmanner the characteristic of scale 12, e. g. linearity, may beaccomplished. In known devices this required accurately machinedfrictional cam drives.

Although an automatic exposure control means for cameras has beendescribed it should be understood that the invention is not limited inits application to cameras. The arrangement according to the inventioncan also be used for controlling the light intensity caused by a constant light source in dependence on a given variable light intensity ofan independent source in such a manner that a between the twointensities there may be effected a desired definite functionalrelationship. As shown in FIG. 2, light-responsive element 1 is lightedby the independent light source, whereas the light of the constantsource 15 is made to enter through diaphragm It). The remainingcomponents of FIGURE 2 are designated in the same manner ascorresponding components of FIGURE 1. As already mentioned, thecharacteristic of scale 12 may be varied in different ways, so that thelight controlled by diaphragm 10 may be controlled in a desired mannerby the intensity of the independent source. By appropriate associationof the sense of rotation and diaphragm movement the exposure can beincreased or decreased with increasing light intensity.

If the light source to be controlled is an artificial source, say anincandescent lamp, the light incidence can be regulated by modifying theintensity of the constant light source instead of by adjustment of thediaphragm 10. For instance, as shown in FIG. 3, this can be done by apotentiometer 13, 19 arranged in the current supply circuit 17 of thelamp 15. This arrangement can be used, according to the invention, e.g.for regulating to a constant value the lighting in a room in dependenceon the incoming day light. In that case, the light-responsive element 1will only be exposed to day light and the electric motor 6 will beconnected to actuate the potentiometer or other current controllingmeans to regulate the intensity of the lamps in the room.

More particularly the invention can be used to make the light from aconstant light source equal to the light intensity derived from anothersource. When the latter intensity changes, this would cause theintensity of the former to change accordingly. The arrangement can alsobe so made that the light intensity from both sources changes in thesame sense, but that the light intensity from the constant source isalways somewhat greater than the intensity of the other source, and anarrangement of this type may be called a light intensifier. As shown inFIGURE 4, the comparison voltage source 4, instead of being a battery,can be a variable source, e.g., a light-responsive element 29 lighted bylight of varying intensity from a light source 21. It is evident then,that within the purview of the invention many variations ormodifications can be made. For example, the diaphragm It) could bereplaced by equivalent means, such as wedges, crossed polarizers, or thelike. Also the gearing between member 7 and the aperture control 9, 10could be replaced by other mechanisms. The invention, therefore, is notto be construed as limited, except as defined in the following claims.

Vve claim:

1. Apparatus for controlling the illuminance produced by a light sourcecomprising a light-responsive element connected across a first resistor,21 source of reference voltage connected across a second resistor, bothof said rcsistors connected in series to the input of an amplifier insuch a way that the voltage drop caused by the lightresponsive elementacross the first resistor opposes the voltage drop caused by the sourceof reference voltage across the second resistor, the output of saidamplifier being connected to an electric motor, two light control meansboth jointly operated by said motor, the first of said light controlmeans arranged so as to vary only the illuniinancc to be controlled butnot the light impinging upon the light-rcsponsive element, the secondlight control means arranged so as to change the amount of lightimpinging upon the light-responsive element.

2. Apparatus according to claim 1, wherein the arm plifier comprises amodulator, an alternating-current amplifier and a demodulator.

3. Apparatus according to claim 1, including a mask having a curvedoutline covering the light-responsive elctent for exposing a curvedportion thereof.

4. Apparatus according to claim 1, wherein the lightresponsive elementis exposed only to the light source producing the illuminance to becontrolled.

5. Apparatus according to claim 1, wherein the lightresponsive elementis exposed to light from a source other than said source producing theilluminance to be controlled.

6. Apparatus according to claim 1, wherein the reference voltage sourceincludes a light-responsive element exposed to light of variableintensity.

References Cited in the file of this patent UNITED STATES PATENTS2,518,717 Rath Aug. 15, 1950 2,655,848 Gray Oct. 20, 1953 2,633,402Bruck July 13, 1954 2,745,021 Kurshan ay 8, 1956

1. APPARATUS FOR CONTROLLING THE ILLUMINANCE PRODUCED BY A LIGHT SOURCECOMPRISING A LIGHT-RESPONSIVE ELEMENT CONNECTED ACROSS A FIRST RESISTOR,A SOURCE OF REFERENCE VOLTAGE CONNECTED ACROSS A SECOND RESISTOR, BOTHOF SAID RESISTORS CONNECTED IN SERIES TO THE INPUT OF AN AMPLIFIER INSUCH A WAY THAT THE VOLTAGE DROP CAUSED BY THE LIGHTRESPONSIVE ELEMENTACROSS THE FIRST RESISTOR OPPOSES THE VOLTAGE DROP CAUSED BY THE SOURCEOF REFERENCE VOLTAGE ACROSS THE SECOND RESISTOR, THE OUTPUT OF SAIDAMPLIFIER BEING CONNECTED TO AN ELECTRIC MOTOR, TWO LIGHT CONTROL